He often wondered if two mirrors were placed opposite each other with no object in between, what if anything would be reflected.

To that end he installed two mirrors in his hallway, one of which was a two-way looking glass, behind which he cut a peep-hole to observe.

At first he saw nothing ... and then ... roving shadow-like wisps of shapes. The shapes steadily increased until he sensed they were sentient to him.

He became unnerved enough that he stopped his experiment, plugging up the hole, removing the mirrors. He just couldn't shake the feeling that there was someone or "something" perpetually behind his back.